1. Technical Field
The present invention relates to a fuel cell, and more specifically to a fuel cell having the flow direction of a fuel gas opposed to the flow direction of an oxidizing gas.
2. Background Art
In a fuel cell, for example, polymer electrolyte fuel cell, reactive gases (fuel gas and oxidizing gas) are respectively supplied to a pair of electrodes (anode and cathode) disposed across an electrolyte membrane to cause electrochemical reactions, so that chemical energy of the matter is directly converted to electrical energy.
Drying the fuel cell lowers the ion conductivity of the electrolyte membrane and thereby degrades the power generation performance. In order to prevent such degradation of the power generation performance of the fuel cell, the reactive gases may be humidified with a humidifier, before being supplied to the fuel cell.
A fuel cell having the flow direction of the fuel gas opposed to the flow direction of the oxidizing gas (counter-flow type fuel cell) is known as the fuel cell that can prevent drying-induced degradation of the power generation performance without using a humidifier. In the fuel cell having the flow direction of the fuel gas opposed to the flow direction of the oxidizing gas, the downstream region along the flow direction of the oxidizing gas on the cathode side faces the upstream region along the flow direction of the fuel gas on the anode side. Water (water vapor) generated by the electrochemical reaction on the cathode is thus transferred from the downstream region along the flow direction of the oxidizing gas on the cathode side to the upstream region along the flow direction of the fuel gas on the anode side. Further transfer of the water vapor on the fuel gas flow to the anode side protects the whole fuel cell from drying and accordingly prevents degradation of the power generation performance.    JP 2008-98181A    JP 2009-4230A    JP 2005-251699A    WO 2006/43394A